The present invention is directed to a hot-rolled steel bar, such as a concrete reinforcing bar, to a method of producing such a steel bar, and to the apparatus for carrying out the method.
Hot-rolled ribbed concrete reinforcing steel bars are used for improving the composite action in concrete where the surface of the bar is provided with ribs forming a partial thread on which an anchoring or connecting member containing a corresponding internal thread can be secured. Based on the fundamental concept of the arrangement of such ribs, steel bars are known suitable for use as concrete reinforcing bars, particularly prestressing bars, where the ribs are located on two opposite sides of the circumference of the bar and extend only along a portion of the circumference of the bar, note DE-PS 17 84 630. Such steel bars can be rolled, in a normal hot rolling procedure, in the last rolling pass by means of a two-high roll pair where it is possible to adjust one of the rolls by rotating it around its axis relative to the other roll whereby determined locations on its circumference can be exactly positioned relative to corresponding locations on the circumference of the opposite roll when the rolls are driven at the same circumferential speed. In this manner, the ribs can be formed on the opposite sides of the steel bar with the ribs being located along a continuous helical line forming a screw thread.
Such steel bars can be used as concrete reinforcing bars if the shape and dimensions of the ribs correspond to the requirements of ribbed concrete reinforcing steel bars with regard to bonding characteristics. Further, such bars can be utilized as prestressing bars for a prestressed concrete structure, and also as anchor bars or rods for ground and rock anchors. Furthermore, such bars can be used as formwork ties or the like. This variety of uses is possible, since anchoring bodies can be screwed on at particular locations of the partial thread formed by the ribs. Such bars have the disadvantage that the anchoring and connecting members to be screwed on them for transmitting a predetermined bar strength must have a greater length than would be the case of a bar with a continuous uninterrupted thread.